The invention relates to a thermal dye transfer print comprising a protective overlayer including a polymeric binder containing dispersed heat expandable microspheres wherein the expandable microspheres have been selectively expanded in a predetermined pattern.
U.S. Pat. No. 6,092,942 (Koichi et al.) includes a thermal dye donor element composed of a yellow, magenta and cyan dye patch plus a protective overlayer which is applied to the receiver layer containing the printed image by means of a thermal print head. The protective layer is applied by using an image plane as a mask as opposed to a uniform application of energy down the page. The protective layer image is designed to have low and high energy arranged in a pattern to produce corresponding regions of density in the transferred protective layer. The final pattern in the transferred protective layer imparts a satin or matte like appearance to the surface of the dye receiver by changing the thickness of the protective layer. The use of a protective layer made in this manner limits the coarseness of the texture that can be applied.
U.S. Pat. No. 6,346,502 (Simpson et al.) and UK Patent Specification 2,348,509 (Lum et al.) teach the use of expandable microspheres in a protective layer to impart a satin or matte finish to dye-diffusion thermal transfer prints. The application of heat during transfer of the protective layer from the donor element to the receiver layer causes the microspheres, which are filled with an easily vaporized fluid, to expand in size. The larger size microspheres scatter light more efficiently giving the appearance of a satin or matte finish to the print. The level of gloss may be controlled by the amount of heat applied to the layer. Application of the protective layer can be done with a thermal print head or other devices, such as a heated roller.
It is a problem to be solved to provide a protective overlayer for a dye transfer print that enables a broader range of patterned textures to be applied to the overlayer.
The invention provides a thermal dye transfer print bearing a protective overlayer comprising a polymeric binder containing dispersed heat expandable microspheres wherein the expandable microspheres have been selectively expanded in a predetermined pattern. The invention also provides a process for making such prints.
The invention enables a broad range of patterned textures to be applied to the overlayer.
As used herein the term xe2x80x9cpatternedxe2x80x9d means a macroscopic pattern in which the pattern present in one square centimeter is not the same as in every other square centimeter of the overlayer. xe2x80x9cMicrospheresxe2x80x9d means generally spheroidal or ellipsoidal shaped beads of expandable material.
The invention is summarized above. It encompasses a thermal dye transfer print bearing a protective overlayer comprising a polymeric binder containing dispersed heat expandable microspheres wherein the expandable microspheres have been selectively expanded in a predetermined pattern and a process for making the same. Suitably, the print of the invention is one wherein the pattern is a macroscopic textile-like repeating pattern. Alternatively, the pattern is an information-bearing pattern especially one that is machine readable or is humanly readable visually or by touch. The protective overlayer may further suitably comprise inorganic particles such as silica particles.
The print of the invention encompasses overlayer arrangements wherein the microspheres are selectively expanded or not depending on a macroscopic location and wherein the microspheres are selectively expanded by various degrees of expansion depending on location.
The print of the invention includes overlayer arrangements wherein the protective overlayer additionally comprises an IR absorbing dye or where the thickness of the protective overlayer varies.
The process for forming the overlayer on a thermal dye transfer print comprises:
1) applying to the print a solid sheet comprising a polymeric binder containing dispersed heat expandable microspheres; and
2) applying heat selectively to the surface of the overlayer sheet so that the expandable microspheres are selectively expanded in a predetermined pattern.
Suitably, in the process of the invention the heat is applied via a thermal print head, especially one where the thermal print head is variable as to which pixels are energized and/or the extent to which pixels are energized. The thermal print head used to heat the protective overlayer is desirably a separate print head from that used to transfer the imaging dye. Alternatively, the overlayer contains an IR dye and the heat is applied via selective application of a laser beam.
Any dye can be used in the dye layer of the dye-donor element of the invention provided it is transferable to the dye-receiving layer by the action of heat. Especially good results have been obtained with sublimable dyes. Examples of sublimable dyes include anthraquinone dyes, e.g., Sumikaron Violet RS(copyright) (Sumitomo Chemical Co., Ltd.), Dianix Fast Violet 3R FS(copyright) (Mitsubishi Chemical Industries, Ltd.), and Kayalon Polyol Brilliant Blue N BGM(copyright) and KST Black 146(copyright) (Nippon Kayaku Co., Ltd.); azo dyes such as Kayalon Polyol Brilliant Blue BM(copyright), Kayalon Polyol Dark Blue 2BM(copyright), and KST Black KR(copyright) (Nippon Kayaku Co., Ltd.), Sumikaron Diazo Black 5G(copyright) (Sumitomo Chemical Co., Ltd.), and Miktazol Black 5GH(copyright) (Mitsui Toatsu Chemicals, Inc.); direct dyes such as Direct Dark Green B(copyright) (Mitsubishi Chemical Industries, Ltd.) and Direct Brown M(copyright) and Direct Fast Black D(copyright) (Nippon Kayaku Co. Ltd.); acid dyes such as Kayanol Milling Cyanine 5R(copyright) (Nippon Kayaku Co. Ltd.); basic dyes such as Sumiacryl Blue 6G(copyright) (Sumitomo Chemical Co., Ltd.), and Aizen Malachite Green(copyright) (Hodogaya Chemical Co., Ltd.); 
or any of the dyes disclosed in U.S. Pat. No. 4,541,830, the disclosure of which is hereby incorporated by reference. The above dyes may be employed singly or in combination to obtain a monochrome. The dyes may be used at a coverage of from about 0.05 to about 1 g/m2 and are preferably hydrophobic.
A dye-barrier layer may be employed in the dye-donor elements of the invention to improve the density of the transferred dye. Such dye-barrier layer materials include hydrophilic materials such as those described and claimed in U.S. Pat. No. 4,716,144.
The dye layers and protection layer of the dye-donor element may be coated on the support or printed thereon by a printing technique such as a gravure process.
A slipping layer may be used on the back side of the dye-donor element of the invention to prevent the printing head from sticking to the dye-donor element. Such a slipping layer would comprise either a solid or liquid lubricating material or mixtures thereof, with or without a polymeric binder or a surface-active agent. Preferred lubricating materials include oils or semi-crystalline organic solids that melt below 100xc2x0 C. such as poly(vinyl stearate), beeswax, perfluorinated alkyl ester polyethers, poly-caprolactone, silicone oil, poly(tetrafluoroethylene), carbowax, poly(ethylene glycols), or any of those materials disclosed in U.S. Pat. Nos. 4,717,711; 4,717,712; 4,737,485; and 4,738,950. Suitable polymeric binders for the slipping layer include poly(vinyl alcohol-co-butyral), poly(vinyl alcohol-co-acetal), polystyrene, poly(vinyl acetate), cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate or ethyl cellulose.
The amount of the lubricating material to be used in the slipping layer depends largely on the type of lubricating material, but is generally in the range of about 0.001 to about 2 g/m2. If a polymeric binder is employed, the lubricating material is present in the range of 0.05 to 50 weight %, preferably 0.5 to 40 weight %, of the polymeric binder employed.
Any material can be used as the support for the dye-donor element of the invention provided it is dimensionally stable and can withstand the heat of the thermal printing heads. Such materials include polyesters such as poly(ethylene terephthalate); polyamides; polycarbonates; glassine paper; condenser paper; cellulose esters such as cellulose acetate; fluorine polymers such as poly(vinylidene fluoride) or poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as polyoxymethylene; polyacetals; polyolefins such as polystyrene, polyethylene, polypropylene or methylpentene polymers; and polyimides such as polyimide amides and polyetherimides. The support generally has a thickness of from about 2 to about 30 xcexcm.
The dye-receiving element that is used with the dye-donor element of the invention usually comprises a support having thereon a dye image receiving layer. The support may be a transparent film such as a poly(ether sulfone), a polyimide, a cellulose ester such as cellulose acetate, a poly(vinyl alcohol-co-acetal) or a poly(ethylene terephthalate). The support for the dye-receiving element may also be reflective such as baryta-coated paper, polyethylene-coated paper, white polyester (polyester with white pigment incorporated therein), an ivory paper, a condenser paper or a synthetic paper such as DuPont Tyvek(copyright).
The dye image-receiving layer may comprise, for example, a polycarbonate, a polyurethane, a polyester, poly(vinyl chloride), poly(styrene-co-acrylonitrile), polycaprolactone or mixtures thereof. The dye image-receiving layer may be present in any amount which is effective for the intended purpose. In general, good results have been obtained at a concentration of from about 1 to about 5 g/m2.
As noted above, the dye donor elements of the invention are used to form a dye transfer image. Such a process comprises imagewise heating a dye-donor element as described above and transferring a dye image to a dye receiving element to form the dye transfer image. After the dye image is transferred, the protection layer is then transferred on top of the dye image.
The dye donor element of the invention may be used in sheet form or in a continuous roll or ribbon. If a continuous roll or ribbon is employed, it may have only one dye or may have alternating areas of other different dyes, such as sublimable cyan and/or magenta and/or yellow and/or black or other dyes. Such dyes are disclosed in U.S. Pat. Nos. 4,541,830; 4,698,651; 4,695,287; 4,701,439; 4,757,046; 4,743,582; 4,769,360 and 4,753,922, the disclosures of which are hereby incorporated by reference. Thus, one-, two-, three- or four-color elements (or higher numbers also) are included within the scope of the invention.
In a preferred embodiment of the invention, the dye-donor element comprises a poly(ethylene terephthalate) support coated with sequential repeating areas of yellow, cyan and magenta dye, and the protection layer noted above, and the above process steps are sequentially performed for each color to obtain a three-color dye transfer image with a protection layer on top. Of course, when the process is only performed for a single color, then a monochrome dye transfer image is obtained.
Thermally expandable microspheres or beads, such as those manufactured as Expancel(copyright) by Expancel, Inc., having an average diameter of from six to seventeen microns can be used to impart a matte or textured finish within the scope of this invention. An average diameter of from six to nine microns in the unexpanded state is preferable. Also, it is preferable that the polymeric wall of the microsphere have a softening temperature between 95 and 130xc2x0 C. and be resistant to attack by solvents commonly used in the preparation of solutions for gravure coating.
Thermal printing heads, which can be used to transfer dye from the dye-donor elements of the invention, are available commercially. There can be employed, for example, a Fujitsu Thermal Head FTP-040 MCSOO1, a TDK Thermal Head LV5416 or a Rohm Thermal Head KE 2008-F3.
A thermal dye transfer assemblage of the invention comprises
(a) a dye-donor element as described above, and
(b) a dye-receiving element as described above, the dye receiving element being in a superposed relationship with the dye donor element so that the dye layer of the donor element is in contact with the dye image-receiving layer of the receiving element.
The above assemblage comprising these two elements may be pre-assembled as an integral unit when a monochrome image is to be obtained. This may be done by temporarily adhering the two elements together at their margins. After transfer, the dye-receiving element is then peeled apart to reveal the dye transfer image.
When a three-color image is to be obtained, the above assemblage is formed on three occasions during the time when heat is applied by the thermal printing head. After the first dye is transferred, the elements are peeled apart. A second dye-donor element (or another area of the donor element with a different dye area) is then brought in register with the dye-receiving element and the process is repeated. The third color is obtained in the same manner. Finally, the protection layer is applied on top.